1. Field of the Invention
The invention concerns a needle-less injector in the form of a hand-held unit, preferably of miniature type, with which a liquid is intracutaneously injected for example into human or animal tissue. The invention aims to expand the area of use of an injector of that kind.
2. Related Art
Liquids in the sense of the present invention are preferably solutions, suspensions or dispersions which contain an active substance. Active substances can be pharmacologically active substances for treatment of the human or animal body or they may be substances for diagnostic or cosmetic uses.
Active substances for non-pharmaceutical uses can be, for example, in the area of plant protection insecticides, fungicides, growth-promoting or growth-inhibiting agents or fertilizers. The needle-less injector according to the invention permits the environmentally friendly application of agents with a systemic action, as the active substance is applied directly to the plant.
EP 0 063 341 and EP 0 063 342 disclose a needle-less injector which includes a piston pump for expelling the liquid to be injected, which is driven by a motor by means of a pressure agent. The liquid container is mounted laterally to the piston pump. The amount of liquid required for an injection is sucked into the pump chamber by way of an inlet passage and a flap check valve when the piston is retracted. As soon as the piston is moved in the direction of the nozzle body the liquid is urged through the outlet passage to the nozzle and expelled. The piston of the piston pump is a solid round piston.
EP 0 133 471 describes a needle-less vaccination unit which is operated with carbon dioxide under pressure, from a siphon cartridge by way of a special valve.
EP 0 347 190 discloses a vacuum compressed gas injector in which the depth of penetration of the injected drug can be adjusted by means of the gas pressure and the volume of the drug can be adjusted by way of the piston stroke.
EP 0 427 457 discloses a needle-less hypodermic syringe which is operated by means of compressed gas by way of a two-stage valve. The injection agent is disposed in an ampoule which is fitted into a protective casing secured to the injector housing. The ampoule is fitted on to the end of the piston rod. Disposed at the other end of the ampoule is the nozzle whose diameter decreases towards the end of the ampoule.
WO 89/08469 discloses a needle-less injector for one-off use. WO 92/08508 sets forth a needle-less injector which is designed for three injections. The ampoule containing the drug is screwed into one end of the drive unit, with the piston rod being fitted into the open end of the ampoule. At its one end, the ampoule contains the nozzle through which the drug is expelled. A displaceable closure plug is provided approximately at the center of the length of the ampoule. The dose to be injected can be adjusted by changing the depth of the ampoule. The piston rod which projects from the drive unit after actuation of the injector is pushed back by hand. Both units are operated with compressed gas.
WO 93/03779 discloses a needle-less injector with a two-part housing and a liquid container which is fitted laterally to the unit. The drive spring for the piston is stressed by means of a drive motor. The spring is released as soon as the two parts of the housing are displaced relative to each other by pressing the nozzle against the injection location. Respective valves are provided in the intake passage for the liquid and in the outlet of the metering chamber.
WO 95/03844 discloses a further needle-less injector. It includes a liquid-filled cartridge which at one end includes a nozzle through which the liquid is expelled. At the other end the cartridge is closed by a cap-type piston which can be pushed into the cartridge. A piston which is loaded by a prestressed spring, after release of the spring, displaces the cap-type piston into the cartridge by a predetermined distance, with the amount of liquid to be injected being expelled in that case. The spring is triggered as soon as the nozzle is pressed sufficiently firmly against the injection location. This injector is intended for one-off or repeated use. The cartridge is arranged in front of the spring-loaded piston and is a fixed component of the injector. The position of the piston of the injector which is intended for a plurality of uses is displaced after each use by a distance in a direction towards the nozzle. The piston and the drive spring cannot be reset. The prestressing of the spring is initially sufficiently great to expel the entire amount of liquid in the cartridge all at once. The spring can only be stressed again if the injector is dismantled and the drive portion of the injector assembled with a fresh, completely filled cartridge.
In some known design configurations of the needle-less injector the supply container for the liquid to be injected is arranged laterally beside the drive unit. The amount of liquid to be injected is sucked into the pump chamber when the solid piston of the piston pump is retracted. The inlet passage includes an inlet valve and the outlet passage includes an outlet valve. Both valves operate with an auxiliary force.
In other design configurations of the needle-less injector the supply container for the liquid to be injected serves directly as a pump chamber and is subjected to the sudden application of force which occurs upon expulsion of the amount of liquid to be injected.
In the case of the needle-less injectors which are operated with compressed gas, a part of the compressed gas escapes after each injection. The compressed gas container is possibly replaceable but it cannot be directly filled with compressed gas again. With such injectors, the drive unit has to be replaced as soon as the compressed gas container is empty.
Accordingly the object is that of providing a multi-use needle-less injector of a simple design, which is preferably suited for repeated expulsion of a predetermined amount of liquid. The amount of liquid which is expelled overall after many uses should preferably be greater than the amount of liquid contained in a supply container. It should be possible for either a plurality of partial amounts of the liquid to be successively dispensed from the supply container or for the amount of liquid contained in a supply container to be taken as a whole and expelled all at once. The supply container should be able to be replaced in a simple manner. A sufficiently great mechanical thrust force (impulse) is to be imparted to the predetermined amount of liquid so that the predetermined amount of liquid penetrates a membrane, a foil or biological tissue.